1. Field of the Invention
The invention concerns a process and an installation for separating non-magnetic materials and objects with the use of magnetic fluids subject to a magnetic field, according to the principle of sink-float separation in one or more separation chambers. The materials or objects which are to be separated are of varying densities, and according to this difference in density are subject to varying forces.
The invention furthermore concerns the composition, manufacture and use of environmental-friendly diluted magnetofluids, where magnetic iron oxide particles, mainly consisting of magnetite, are, through a monomolecular fatty acid layer and through a second layer of alcoxylated fatty alcohols and end-group sealed alcoxylated fatty alcohols or by sugar surfactants, protected against agglomeration and colloidally dispersed in water. Through the addition of water-soluble substances, which are capable of creating extra hydration effects, the sedimentation stability can be improved.
The invention is especially applicable for separating substances of various materials or objects, for ample during the recycling of electronic scrap or automobile scrap, during ore or coal processing or similar separation processes. The environment-friendly diluted magneto-fluids are especially suitable for the sink-float separation of non-magnetic substances, but also as calibration fluids for magnetic measuring instruments, as sealing fluids for hermeticaly sealing rotary appliances, as lubricants and as marking substances in agriculture and forestry for the analysis of soil erosion, as well as for use in medicine.
The principle of the sink-float separation of non-magnetic materials in magnetic fluids in the magnetic field gradient has long been familiar. However, until now the feasibility of this process has foundered on the magnetic fluids available, their insufficient attributes, the processing costs, and on the lack of interest in disposal and recycling problems.
2. Description of Related Art including information disclosed under 37 CFR 1.97-1.99.
DE 3124276 C2 describes a process and installation for separating non-magnetic solid materials of varying density, which are suspended in a magnetic fluid and are conveyed in the fluid through a separation zone with a gap tapering into a V-shape, in which magnetic lifting forces, different from the adjacent areas, are at work. The magnetic field is created by a set of magnets, which under formation of the V-shape are placed with their pole surfaces opposite each other. By means of this solution non-magnetic materials can be classified without size limitation, by conveying the material crosswise to the lengthwise direction of the obliquely downward sloping and tipped V-gap at the upper end of the separation zone, and by separating the material components of higher density in the area of the V-gap; meanwhile the material components of lower density are suspended and conveyed above the V-gap into the lower area of the sloping separation zones.
U.S. Pat. No. 4,521,303 describes a process for separating a mixture of carbon and other solid components by means of magnetic fluids through a described circulation regime.
Concrete installations for substance separation by means of magnetic fluids, or improvements of the single components of such installations have been described, for instance, in the following publications: DE U.S. 2509959 and DE 3324536 C2 structure of the magnetic poles); DE 3321102 C2 (structure of the separation cell) and U.S. Pat. No. 4,113,608 (inletting and outletting of the product to be separated).
The disadvantage of all the familiar solutions is that a recovery of discharged magnetic fluid and a constant maintenance of the concentration and volume of the magnetic fluid in the separation cell is not possible or not accounted for. There is the further disadvantage that the separation is limited to fragmented materials.
Through the development of innovative magnetic fluids the prerequisites for a major technical deployment of the sink-float separation process by means of magnetic fluids have been improved.
Magneto-fluids are dispersions of small magnetic particles in optional carrying fluids. The carrying fluids are chosen according to the purpose of the magneto-fluids. In order to maintain stable magneto-fluids, the magnetic particles must be colloidally dispersed in the carrying fluid. An agglomeration of these particles is frequently prevented through one or more adsorption layers of surface-active substances; their type is again determined by the carrying fluid and the demands put on the magneto-fluid.
The magnetic characteristics of these superparamagnetic fluids depend on the type, size and concentration of the magnetic particles. All other characteristics are determined by the carrying fluid, the surface-active substances, and solubilizers, which may have to be added to improve solubility and stability.
From DD 292 825 A7, for example, a magnetic fluid is known to exist, which is produced on a mineral oil base and can be especially applicable for the sealing of rotary appliances, for magneto-fluid storage and for the damping of oscillation coils.
A process of manufacturing a ferro-fluid on oil, ester, or ether base, is described in DE 33 12 565 C2.
Furthermore, there are numerous formulations encountered in the literature on patents concerning diluted magneto-fluids, where the magnetite particles have been stablised mostly through a monomolecular adsorption layers consisting of one or more fatty acids and a second layer of one or more anionic, cationic, amphoteric or non-ionic surfactant. For instance, the following substances were used as a second layer: fatty acids (U.S. Pat. No. 4,208,294), sulphone acids or sulphates (U.S. Pat. No. 4,094,804, U.S. Pat. No. 4,855,079). All the variants have the disadvantage that no magneto-fluids are produced that are neutral or stable, or not easily soluble, in a neutral ambience. As regards the use of cationic or amphoteric surfactants, this equally applies on principle, or the chemical compounds are based on those which are not completely harmless ecologically, or even toxologically speaking (U.S. Pat. No. 4,493,778; DE 37 09 852 A1).
DE 37 09 852 A1 describes stable magnetic fluid compounds with characteristics such as the capability of conducting electricity, ion exchange capacity, and anti-microbial effetivity. There are, however, only few concrete, feasible examples cited, and these do not purport the manufacture of diluted magneto-fluids. With some of these surfactant classes, as is also described in U.S. Pat. No. 4,938,886, there are indeed some more or less easily biologically degradeable, non-toxic and neutrally soluble diluted magneto-fluids that can be manufactured; however, these special surfactants, not available commercially, have to be synthesised in an expensive and elaborate process. For the manufacture of larger amounts of magneto-fluids, which, for example, are necessary for separation apparatus using the sink-float process with about 1 tonne of scrap throughput per hour, such special surfactants are financially out of the question. An economically more viable variant is described in DE 41 30 268 A1. However, one falls back here on alkylarylpolyetherglycins, which are not completely without their problems of ecological feasibility. Apart from which, the adsorbed monolayer is made of carboxyl-functionalised polymers, which are not easily, biologically degradeable.